Motor vehicle collisions with pedestrians and bicyclists are a significant concern. While significant advancements have been made in protecting motor vehicle occupants from injury due to impacts, there remain significant opportunities to reduce injuries, particularly head injuries to pedestrians struck by motor vehicles. Various countermeasure systems have been devised for this purpose and are in use. Hood lifter mechanisms pop the engine compartment hood to an upward displaced position where it can absorb energy as a struck pedestrian hinges about their lower torso and strikes the hood area during an impact. The lifted hood provides energy absorption. Other measures such as external airbags have further been conceived and implemented. In this description, reference to pedestrian impacts is intended to include other types of impacts including those with bicyclists or animals and other low-energy (as compared with striking other vehicles or fixed objects) impacts.
For any deployable pedestrian impact countermeasure to be operative, some means of detecting the impact is required. Numerous systems are available for detecting such impacts. One approach uses an elongated flexible hollow tube which defines an enclosed volume of gas, typically air. Upon an impact, the soft fascia of the vehicle front end is deformed and the sensor tube is compressed, generating a gas pressure pulse in the tube which is transmitted to a pressure sensor, thereby detecting the impact. For these systems to be operative, a supporting structure behind the pressure based sensor is necessary. This structure enables the necessary compression to occur for generating the pressure pulse. Numerous other sensor technologies may be implemented which measure strain or compression exerted by deformation of the vehicle front end fascia. For example, other types of low energy impact sensing systems include switch arrays, peizo cable, fiber optic, etc. All such sensing techniques based on compression or deformation will be referred herein as compressive or compression sensors.
A particular design challenge is posed in extending the sensitive area of the vehicle front end to low energy impacts to include the outer corners or edges of the front end (referred in this description also as the boundaries of the front end). Typical passenger car and light truck vehicles feature rounded front end corners which create a glancing or oblique impact if the pedestrian strikes the vehicle in these areas. The glancing impact may not provide sufficient compression for a compression sensor to be operative as well as acting as part of the vehicle's high energy impact system. Moreover, typical vehicle front ends feature an energy absorbing cross beam in the front end needed for meeting low speed impact requirements. The structure of the energy absorbing beam may not extend laterally to these outer front corners. Accordingly, it is often the case that an underlying structure necessary for creating a reaction force to the impact resulting in compression of the sensing system in these outer corner areas is absent.
With the increasing demand for implementation of active pedestrian protection systems and improved frontal sensing capabilities, the packaging and detection capabilities are becoming more complex. Sensors required to detect events such as pedestrian impacts are packaged close to the front of the vehicle, and require accommodations for vehicle styling as well as bumper sensing area coverage. As compressive sensing technologies are introduced into the front end system of the vehicle, integration concepts to support the sensing technology are evolving. Body components such as fascia, energy absorber, and bumper beams are becoming key components in the impact energy transfer function.
Vehicle front end components are designed to meet damageability and injury criteria requirements, but generally do not consider requirements for pedestrian impact sensor integration or applications as a primary design objective. To meet the damageability and injury criteria requirements, the component suppliers incorporate a design balance of component stiffness versus compressibility. This balance can result in non-linear load transfer characteristics that make the integration of a compressive sensor technology complicated. It is critical that a compressive sensor assembly, in its installed condition in a motor vehicle structure, be properly tuned to respond to impacts of prescribed characteristics. Although it is possible to design compressive sensors having inherent sensitivity characteristics, such a sensor may not be adaptable for use over multiple vehicle product lines. In addition, it is often necessary to adjust the sensitivity and response of a compressive sensor along its extended length due to changes in the types of impact occurring at various areas of the vehicle and the characteristics of underlying and supporting structure.
In view of the aforementioned, there is a need in the art for improved pedestrian impact system which addresses the previously mentioned shortcomings in prior art systems. In particular, the need exists to enable flexibility in adjusting the sensitivity or tuning of a compressive sensor which is highly adaptable, and provides repeatable characteristics.
In any volume produced automotive application, cost concerns are significant. The increased sophistication and capabilities of motor vehicles must be provided in an efficient and low cost manner in order that the features become commercially viable. Accordingly, systems provided to meet the design objectives mentioned above need to be manufacturable and capable of being assembled in a cost effective manner.